Heat producing equipment such as, for example, electronic power inverters and converters are frequently subjected to very high ambient temperatures which may have an adverse affect on the life, reliability and/or performance of the equipment. Several systems are available for the cooling or conditioning of the air in the electronic enclosures. The technology used for cooling relate to and include passive cooling systems, conventional compressor-based systems and thermoelectric systems.
In passive cooling systems, the air to be cooled is circulated over an air-to-air heat exchanger, which includes folded, finned heat exchangers, heat pipes, etc. The heat is then exchanged with the outside ambient air. As the amount of heat to be removed from the enclosure increases, the size of the air-to-air heat exchanger must be increased in size. Another drawback of the passive cooling system is that the amount of heat the system can remove from the enclosure is determined by the ambient temperatures of the air surrounding the enclosure. Therefore, if the ambient temperature is at, for example, 55° C., the temperature inside the enclosure can only be lowered to a temperature slightly above the ambient temperature by the passive cooling system.
Compressor based systems function by using a refrigerant and the cooling function is achieved by the compression and expansion of the refrigerant. The compressor based systems are efficient but are bulky, have large maintenance costs and consume large amounts of electricity. Also, all the cooling is done actively, which may not be necessary when, for example, the ambient outside air is sufficiently cool.
Thermoelectric temperature control systems use thermoelectric devices that pump heat using the Peltier effect. The thermoelectric devices are highly reliable and very economical at low wattage applications. As the number of watts to be removed are increased, the cost of this type of system increases as the cost is directly related to the number of thermoelectric devices that are needed for the particular function. The cooling capacity may be limited because of the power supply requirements since more thermoelectric devices necessitates more power.
The most typical thermoelectric device incorporates a thermoelectric module/component that utilizes electrical current to absorb heat from one side of the module and dissipate that heat on the opposite side. If the current direction is reversed, so is the heat pumping. Generally, cold sides and hot sides are developed necessitating an effective means of removing or adding heat from or to a solid, liquid or a gas (typically air).
U.S. Pat. No. 5,890,371 describes a hybrid air conditioning system that includes a passive heat removal system in conjunction with a thermoelectric temperature control system for conditioning the air in an enclosure. The passive heat removal system pre-cools warm or heated air. The pre-cooled air then flows through and over the thermoelectric temperature control system. The passive heat removal system includes a heat pipe or phase change type of heat exchanger that includes a passive evaporator connected by a pipe to a passive condenser. The heat pipe or heat pipe system is preferably a vacuum-type vessel that is evacuated and partially filled with an operational amount of working fluid, which evaporates at a low temperature. As heat is directed into a portion of the evaporator, the working fluid is vaporized creating a pressure gradient in the heat pipe system. This pressure gradient forces the vapor to flow along the pipe to the cooler section (the condenser) where it condenses, giving up its latent heat of vaporization. The working fluid is then returned to the evaporator by capillary forces developed in the heat pipe's porous wick structure, or by gravity.
It would be advantageous to provide a system that can control the temperature of the air in electronic enclosures in an improved manner, which would enable lower cost, increased reliability and efficiency, and low maintenance.